Various embodiment of the invention relate generally to a directional magnetometer and particularly to a MEMS Lorentz force magnetometer
A directional magnetometer is a sensor that measures magnetic field along an axis. An ideal in-plane magnetometer is sensitive to magnetic field that is parallel to the planar geometry of the magnetometer. An ideal out-of-plane magnetometer is sensitive to magnetic field in the direction perpendicular to the planar geometry of the magnetometer. For high volume, low cost production it is advantageous to use the same fabrication methods as other micro-machined inertial sensors like accelerometers and gyroscopes. A MEMS Lorentz force magnetometer is such a sensor.
A MEMS Lorentz force magnetometer has a drive subsystem where an electric current flows through the drive subsystem and a Lorentz force acts on the drive subsystem resulting in motion about a first axis in response to a magnetic field along a second axis substantially parallel to the plane of a substrate.
However, unwanted forces can arise on a MEMS device with a MEMS Lorentz force magnetometer from off axis magnetic field, electronic noise sources, exogenous linear acceleration and other sources. If these forces are not balanced about the rotational axis they will cause motion and will be undesirably detected by the sensing element and misinterpreted as a Lorentz force. They will be indistinguishable from magnetic generated motion and will cause cross axis error, offset and additional noise.
Thus there is a need for MEMS magnetometers to measure magnetic fields with increased accuracy and reduced noise and size.